A. Field of the Invention
The present invention relates to lighting fixtures that produce high intensity, controlled and concentrated light beams for use at relatively distant targets. In particular, the invention relates to an efficiency improvement in the light output of such lighting fixtures. One primary example of use for such fixture with improved output is illumination of a sports field.
B. Issues in the Present State of the Art
Lighting fixtures 10 (refer to FIG. 1A) used for illumination of large areas, such as sports fields 2, are generally comprised of elevated structures 1 with relatively high intensity light discharged from a fixture with reflective material that directs the light onto the target area where it is needed. One such fixture is described in U.S. Pat. No. 4,947,303, incorporated by reference in its entirety herein, and commercialized by Musco Corporation of Oskaloosa, Iowa. It uses a spun aluminum symmetrical reflector attached to a cone. An axially-mounted lamp is inserted through a hole in the back center of the reflector where it engages a socket in the cone.
Another fixture is described in U.S. published patent application 2006/0274532 A1, commercially available from Musco Corporation of Oskaloosa, Iowa, incorporated by reference in its entirety herein. It uses a reflector frame having a main portion generally following a ‘surface of revolution’ of the type that produces a converging beam, and a bottom portion generally following a ‘surface of revolution’ of the type that produces a generally less converging beam. A high total reflectance sheet or multiple piece reflecting layer is placed over the main portion and bottom portion. The result is a low reflective loss reflector of non-symmetrical shape.
A similar fixture is described in U.S. published patent application 2006/0187663 A1, now U.S. Pat. No. 7,740,381, commercially available from Musco Corporation of Oskaloosa, Iowa, incorporated by reference in its entirety herein. It uses a die cast metal reflector frame, somewhat simulating a bowl shape, including an inner surface with mounting structure. A high reflectance sheet or plurality of high reflectance inserts are placed onto the mounting structure to create a reflecting surface, which allows high customizability of the reflecting surface and minimizes light loss.
These fixtures work well. However room for improvement exists in these designs, as well as other designs. Openings or breaks in the reflective surface of the fixture can lead to reduced efficiency. Generally, the most significant example of this is the transition area between the reflector or reflector frame and the cone.
This issue is illustrated in FIG. 4A. To support the axial type lamp 11 and provide electrical connection, the neck 61 of the lamp 11 extends through an opening in the back center of the shell of the reflector 15/150. Due to the curvature of the lamp globe 62 (FIG. 2A), the opening in the reflector material may be larger than needed for the neck 61 alone. The cone 13 (FIG. 4A) contains an internally threaded socket 18 into which can be screwed or unscrewed the threaded metal end 63 (FIG. 2A) on neck 61 of lamp 11. The reflector shell 15 mounts to cone 13 at its rim 131 (see FIG. 3B). The opening through the reflector shell 15 would be somewhat smaller than the diameter of rim 131 of cone 13. Therefore, as indicated in FIG. 4A, an annular gap G would exist around the neck 61 of lamp 11 between the lamp and the edge of the opening in reflector shell 15. Thus, light energy from lamp 11 that travels from its arc tube 31 to gap G would likely not be reflected in a manner that could be controlled and used at the target. This light would thus essentially be wasted for the intended function of fixture 10. While this is a fraction of the total light from light source 31, it is not minuscule and the energy to create it must be paid for, and because it is not controlled it can contribute to glare or spill light which are undesirable effects.
In some fixtures, to help support the lamp 11 when screwed into socket 18 in cone 13, a reinforcing ring 26/28 is installed around the opening between the reflector shell 15 and cone 13. FIG. 2A of the present application indicates how ring 26/28 could be bolted between reflector shell 15 and cone 13 around the opening in reflector shell 15, using a plurality of bolts 64 and nuts 65, FIG. 3B. It could also be assembled such that reflector shell 15 is bolted between ring 26/28 and cone 13.
Ring 26/28 can be a single metal ring (e.g. aluminum). Alternatively, as shown, it can be two rings. The ring(s) 26/28 may be flat. One or both may be somewhat reflective. By the term “somewhat reflective”, it is meant that it may not be totally light absorbing, but typically is light diffusive, meaning that any reflection is not precisely controlled. Therefore, as indicated by several examples of light rays (reference numbers 20, 21 and 22 in FIG. 2A), to the extent light directly from arc source 31 would reflect out of the front of fixture 10, by the laws of reflection, rays 21 and 22 would reflect off the flat, somewhat reflective surface of ring 26/28 in a diverging and not precisely controlled fashion. Because of the relatively long distance from a fixture 10 to a sports field 2, for control of the light it should be converging towards the aiming axis of the fixture. Therefore, this results in much of the light reflecting divergently from the prior art ring 26/28 and thus not being effectively controlled for use to light field 2. It may be wasted. It may contribute to glare and spill light, which is usually undesirable. Additionally, because ring 26/28 at best is only somewhat reflective, the light that is absorbed or is diffusively redirected is also unlikely to be usefully available to light the field, and thus is wasted. This method of construction has been, and still is used by many different manufacturers. However, improvements are needed.
Also, some manufacturers do not use this ring, which leaves the aforementioned gap G open. Light from the light source that goes to this gap is essentially wasted. It could be beneficial to capture and direct this light to the target.